Interhemispheric transfer of visual learning in monkeys with intact optic chiasm.

The purpose of the present experiments was to investigate the role of the forebrain commissures in interhemispheric visual transfer when both eyes are open and the optic chiasm is intact. Cynomolgus monkeys (Macaca fascicularis) learned a series of two-choice simultaneous visual discriminations. The visual stimuli were bipartite, with independently determined left and right halves. If such a stimulus is fixated centrally, the two halves fall into opposite visual hemifields. After 10 trials of acquisition of each discrimination, the same discriminanda were presented for a further 10 trials in which, within each stimulus, the positions of the halves were exchanged: the left half became the right and vice versa. The unoperated animals transferred well to the altered stimuli, making many fewer errors than they made in learning the originally presented discrimination. In contrast, monkeys with section of the posterior corpus callosum and the anterior commissure transferred poorly. These effects show that the forebrain commissures are important for the interhemispheric transfer and integration of visual information in animals with a normal, intact peripheral visual system.